Preparation And Characterization Of Paraffin/Carbon Foam Form-stable Composite Phase Change Materials

Phase change materials(PCMs)have such advantages as larger energy storage density,similar phase change cycle temperature,repeatable utilization,and many other advantages,which can be applied in the field of development and utilization of new energy and development and industrial waste heat recovery.The application of solid-liquid phase change energy storage materials has two technical problems: the instability of phase change process and the low thermal conductivity of phase change materials.Phase change materials leakage will cause damage to the substrate material and reduce mechanical properties;low thermal conductivity will cause the low heat storage of phase change materials and heat release rate decreased,thereby affecting applications.In this paper,using foam carbon substrate packaging paraffin method,combined with thermal performance testing and structural analysis,the main achievements have the following three parts:(1)Preparation of foamed carbon precursor and its micro pore structure.Starch powder is used as raw material,through vacuum freeze-drying method,making into foam carbon precursor.Foam carbon precursor surface can generate an irregular layer structure,and it getting denser as the starch concentration increasing.The foam carbon is prepared by the method of carbothermal reduction.The three-dimensional mesh structure of the foamed carbon can be controlled by the starch concentration and the carbonization temperature.It can be concluded that the sample is not pure amorphous carbon,and a small amount of graphite structure exists.(2)Preparation and analysis of paraffin / foam carbon composite phase change materials(PCF).The experiment was carried out using paraffin as phase change materials,and filled with two common methods: vacuum impregnation and atmospheric pressure adsorption.The optimum immersion time under vacuum condition is 30 minutes,and the optimum adsorption time is 5 hours under atmospheric pressure.Under the vacuum environment,the adsorption rate of paraffin is 99.87 wt%,and the adsorption rate of paraffin wax is 98.74 wt% after atmospheric pressure adsorption experiment.The experimental method of vacuum impregnationcan shorten the preparation time of PCMs and thus improve the preparation efficiency.(3)Paraffin/ carbon foam form-stable composite phase change materials,thermal performance and cycle stability analysis,as well as the calculation and analysis of thermal conductivity.The IR spectra of PCF show that,as composite phase change materials,there is only physical combination between foam carbon and paraffin.The DSC analysis showed that,with the pure solid paraffin,there were two endothermic peaks and two exothermic peaks in each thermal cycle,which corresponded to the solid-solid phase transformation and solid-liquid phase transition of the paraffin respectively.The enthalpy is up to 141.1 J / g.The results of TGA show that the actual reason for the sample mass losing during the heating process is the decomposition of paraffin wax,and the initial decomposition temperature of paraffin wax in each sample is delayed by different degrees.The process of mass loss is prolonged,and the PCF of composite phase change materials has good thermal stability below 176.4 ℃.In more than 200 tests.It was found that in both before and after cycle the internal chemical structure of the composite phase change materials did not change.And the phase transition temperature did not change significantly,which proved that the thermal stability of the composite phase change materials was good.By calculating the thermal conductivity of composite phase change materials,the most significant one is 0.7207 W /(m · K),increased by 3.43 times.The thermal conductivity of the composite phase change materials is obviously improved compared with that of pure paraffin.It indicates that the high specific surface area of the foamed carbon three-dimensional mesh structure can stably encapsulate the organic phase change materials in its pore structure.After carbonization,the three-dimensional carbon network and the carbon film formed inside the foamed carbon are not only provide structure protection,but also increase the material thermal conductivity by using electronic,phonon dual mechanism common effect.